Bending
The bending results are performed with free bending and with normal friction (no lubrication). The table shows the minimum internal bend radius (Ri) that can be obtained without cracks for specific materials and sheet thicknesses (valid for all bending directions). Bending to smaller inner radius than recommended can often be realised but is done at the user’s own risk.
When bending a large number of details lubrication can be of need.
In order to get the best bending results, perform bending with burr on the inside of the sheet (burr is always a crack initiation).
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Pv
Ri
Wd
R
t
L |
Bending force in V-bending
Internal bend radius
Die Width
Punch radius
Workpiece thickness
Workpiece width |
Drawing
Limiting Drawing Ratio (LDR, D/d)
The ability to deep drawing is conventionally carried out by a cup test in which a cup is drawn in a one step operation. A correct blankholding force prevents wrinkling and allows the blank to “flow” between the die and the punch.
The Limiting Drawing Ratio, LDR, is defined as the ratio between the maximum blank diameter (D) which can be drawn to the cup shape without fracture, and the punch diameter (d).
A Blank
B Die
C Blankholder
D Punch
Stretching
Stretch forming capability (H/d)
The stretch forming test over a hemispherical punch is a test metod used by SSAB which resembles the Erichsen test. It is sometimes called dome height test or bulge test.
A circular blank is clamped firmly between the die and the blankholder. It is then stretched to fracture over a 100 mm diameter hemispherical punch.
Stretch forming capability is expressed as the ratio between the maximum height of the stretched dome before fracture (H) and the punch diameter (d).
